The invention relates to a magnetic head for a magnetic recording and playback apparatus, which head comprises a core of a spinel ferrite having two core parts which are spaced from each other and between which a transducing gap is formed.
It is known that the use of spinel ferrites, in particular Mn-Zn ferrites, as a magnetic core material of magnetic heads is desired for use in apparatus for magnetic tape recording and playback, such as audio and video tape recorders, because ferrites are available which have the advantages of a high resistance to detrition and very good magnetic properties, for example, with reference to magnetic saturation, coercive force and permeability, and good frequency characteristics.
Magnetic fields which are generated by a magnetic head at the area of the transducing gap to write information on a magnetic medium depend directly on the saturation magnetization of the material of the magnetic head core. Magnetic heads for present-day video recorders usually have a core of a Mn-Zn ferrite having a characteristic saturation magnetization 4.pi.M.sub.s of approximately 500 mT (5,000 Gauss) at room temperature. Their magnetization, also at temperatures slightly above room temperature, satisfies the requirements imposed by the recording of information on conventional tapes such as CrO.sub.2 tape having a coercive force H.sub.c of approximately 56 k A/m (700 Oersted).
However, in order to improve the quality of the video recording process, there is a tendency to replace the conventional magnetic tapes by magnetic tapes having a high coercive force, for example, tapes on the basis of pure Fe, which have a H.sub.c of approximately 88-136 kA/m (1,100-1,700 Oersted). The use of such magnetic tapes implies that the materials of the magnetic core must have a larger 4.pi.M.sub.s value than the present-day ferrite materials. Such a material does exist but it has other properties which make it less suitable for the applications in view. This material, Sendust, an alloy consisting of approximately 85% by weight of Fe, 10% by weight of Si and 5% by weight of Al, has a saturation magnetisation 4.pi.M.sub.s which is considerably larger than 500 mT (5,000 Gauss). However, it has the disadvantage that, in contact with a moving magnetic tape, it is subject to a much higher detrition than ferrite. Moreover, Sendust has a resistivity of 10.sup.-6 .OMEGA. m (10.sup.-4 .OMEGA. cm), which is three orders of magnitude smaller than that of, for example, monocrystalline Mn-Zn ferrites. Due to this low resistivity, the core of a video-Sendust head must be constructed from a number of thin laminations which are insulated from each other, which complicates production techniques.